Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/tobaccothripsnew6166hook 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  ENTOMOLOGY— BULLETIN  NO.  65. 

L.  O.  HOWARD,  Entomologist  and'Chief  of  Bureau 


THE  TOBACCO  THRIPS, 

A NEW  AND  DESTRUCTIVE  ENEMY  OF 
SHADE-GROWN  TOBACCO. 


W.  A.  HOOKER, 

Special  Field  Agent. 


Issued  April  19,  1907. 

A.. Vv  \ A A , A 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

19  0 7. 


BUREAU  OF  ENTOMOLOGY. 


L.  O.  Howard,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Marlatt,  Entomologist  and  Acting  Chief  in  absence  of  Chief. 
R.  S.  Clifton,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  breeding  experiments. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  cotton  boll  weevil  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage-plant  insect  investigations. 
A.  L.  Quaintance,  in  charge  of  deciduous-fruit  insect  investigations. 

E.  F.  Phillips,  acting  in  charge  of  apiculture. 

D.  M.  Rogers,  in  charge  of  gipsy  and  brown-tail  moth  work. 

A.  W.  Morrill,  engaged  in  white  fly  investigations. 

E.  S.  G.  Titus,  in  charge  of  gipsy  moth  laboratory. 

C.  J.  Gilliss,  engaged  in  silk  investigations. 

R.  P.  Currie,  assistant  in  charge  of  editorial  work. 

Mabel  Colcord,  librarian. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BCREAO  OF  ENTOMOLOGY — BULLETIN  NO.  65. 

L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau 


THE  TOBACCO  THU  IBS, 

A NEW  AND  DESTRUCTIVE  ENEMY  OF 
SH ADE-OROWN  TOBACCO. 

BY 

W.  A.  HOOKER, 

Special  Field  Agent. 


Issfed  April  19,  1907. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

190  7 . 


LETTER  OF  TRANSMITTAL. 


U.  S.  Department  of  Agriculture, 

Bureau  of  Entomology, 
Washington,  D.  C .,  January  31,  1907. 

Sir:  T have  the  honor  to  transmit  herewith  a manuscript  by 
Mr.  W.  A.  Hooker,  special  field  agent  in  this  Bureau,  on  the  tobacco 
thrips,  an  insect  which  has,  during  the  last  two  or  three  years, 
caused  great  damage  to  shade-grown  tobacco  in  Florida,  Texas,  and 
Georgia.  This  paper  contains  a general  account  of  this  thrips,  and 
gives  recommendations  for  applying  remedial  measures,  and  I rec- 
ommend its  publication  as  Bulletin  No.  65  of  the  Bureau  of  Ento- 
mology. 

Respectfully, 


Hon. 


L.  O.  Howard, 

Entomologist  and  Chief  of  Bureau. 

James  Wilson, 

Secretary  of  Agriculture. 


CONTENTS. 


Page. 

Introduction 5 

History : 5 

Nature  and  extent  of  injury 0 

Origin  and  distribution _ 7 

Description 8 

The  adult 8 

The  egg 0 

The  larva 9 

The  young  nymph  or  prepupa 10 

The  full-grown  nymph  or  pupa 10 

Habits 10 

Feeding 10 

Jumping -----  _ -------  11 

Flight 

Food  plants H 

Life  history 11 

Methods  of  study 11 

Life  cycle 12 

Hibernation 12 

Other  thrips  that  may  be  mistaken  for  the  tobacco  tlirips 12 

Natural  control 13 

Rains - 13 

Insects 14 

Remedies 14 

Cultural  methods 14 

Insecticides 17 

The  best  treatment-? 19 

How  to  make  kerosene  emulsion 19 

When  to  apply  the  emulsion - 19 

How  to  use  the  emulsion 20 

Cost  of  spraying 20 

Supplies  and  labor 20 

Apparatus 21 

Summary  of  recommendations 21 

Caution 21 

Addenda 22 

The  tobacco  thrips  in  1905-6 22 

Effect  of  the  spray 22 

Index 23 


3 


IL  LUSTRATIONS. 


PLATES. 

Page. 

Plate  I.  Fig.  1. — Slat-shade  field,  showing  Iron  eowpeas  as  grown  be- 
tween tobacco  crops.  Fig.  2. — Leaf  of  tobacco,  showing 
“white  veins,”  caused  by  the  tobacco  thrips  (Euthrips  nico- 
tian w) 6 

II.  Fig.  1. — Slat-shade  tobacco  field,  showing  seed  bed.  Fig.  2. — 

Cheesecloth-sliade  tobacco  field,  showing  seed  bed 10 

TEXT  FIGURES. 

Fig.  1.  The  tobacco  thrips  (Euthrips  nicotiance ) : adult 8 

2.  Diagram  showing  total  monthly  precipitation  at  Tallahassee,  Fla., 
during  April,  May,  June,  and  July,  1900-1906,  to  illustrate  rela- 
tion of  rainfall  to  amount  of  injury  by  the  tobacco  thrips 15  | 

4 


THE  TOBACCO  THRIPS,  A NEW  AND  DESTRUCTIVE  ENEMY  OK 
SHADE-GROWN  TOBACCO.  ° 

( Euthrips  nicotian  a : Hinds.) 


INTRODUCTION. 

In  accordance  with  the  authorization  of  the  Secretary  of  Agricul- 
ture and  the  instructions  of  Dr.  L.  O.  Howard,  the  writer  left  Wash- 
ington, D.  C.,  April  14,  1905,  to  investigate  certain  injury  to  shade 
tobacco  at  Quincy,  Fla.  He  arrived  at  Quincy  April  16  and  spent 
the  following  two  months  in  the  work.  Having  reached  what  seemed 
to  be  a satisfactory  result,  he  left  there  on  June  16.  June  27  was 
spent  at  Palestine,  Tex.,  and  June  28  and  29  at  Nacogdoches,  Tex.,  in 
examination  of  tobacco  fields.  At  Quincy  the  writer  was  associated 
with  Mr.  W.  W.  Cobey,  tobacco-breeding  expert  of  the  Bureau  of 
Plant  Industry,  from  whom  valuable  advice  and  suggestions  were 
received.  The  writer  again  visited  Quincy  in  October,  1905,  and  spent 
two  weeks  in  a further  examination.  A continuation  of  the  work  was 
planned  for  1906,  but  could  not  be  carried  out,  although  a visit  was 
made  at  Quincy  in  November  to  determine  the  results  obtained 
where  remedial  measures  had  been  employed. 

HISTORY. 

The  first  report  of  thrips  injuring  tobacco  in  this  country,  so  far  as 
the  writer  is  aware,  was  made  by  Dr.  F.  II.  Chittenden  in  1904,* *  6 the 
species  concerned  being  considered  as  Euthrips  tritici  Fitch.  As  will 
be  seen  from  the  following  pages,  additional  material  showed  that 
the  insect  concerned  is  a new  species,  Euthrips  nicotianoe  Hinds. 

A Russian,  Lindeman,®  first  described  scientifically  in  1888  a 
species  of  thrips,  Thrips  tabaci , which  he  reported  as  doing  great 
damage  to  tobacco  in  that  country.  While  this  same  species  is  gen- 
erally distributed  in  our  own  country  and  although  its  list  of  food 
plants  is  large,  it  is  not  recorded  as  having  attacked  tobacco  here. 

Several  communications  were  received  by  this  Bureau  during  the 

a Circular  No.  68,  published  February,  1906,  gives  a brief  account  of  the 

insect  and  remedies  recommended  by  the  writer. 

& Yearbook  of  the  U.  8.  Department  of  Agriculture  for  1904,  p.  605,  1905. 

c Die  Schadlichsten  Insekten  des  Tabak  in  Bessarabien,  Bull.  Soc.  Imp. 
Natur.,  Moscow,  pp.  51-65.  1888.  See  also  Targioni-Tozzetti,  Animal!  ed 

insetti  del  Tabacco,  pp.  222-224,  1891. 


6 


THE  TOBACCO  THRIPS. 


summer  of  1904,  with  inquiries  concerning  an  injury  to  shade-grown 
tobacco  in  Florida.  The  insect  causing  this  injury  was  variously  " 
described  as  “ a little  parasite,”  “ a flea,”  “ an  unknown  insect,”  etc.  * 
Not  until  the  winter  of  1904  could  anything  definite  be  learned.  At 
that  time  a report  Avas  received  from  Mr.  W.  W.  Cobey,  tobacco- 
breeding expert,  of  the  Bureau  of  Plant  Industry,  describing  the 
nature  of  the  injury. 

It  seems  that  on  tobacco  grown  in  the  South,  and  under  shade  espe-  I 
cially,  insect  enemies  of  the  crop  are  found  at  their  worst.  Of  the 
many  insects  with  which  the  planter  has  had  to  deal  in  the  past,  the  | 
budworm,  requiring  tAvo  and  three  applications  a week  of  arsenicals, 
has  been  far  in  the  lead  in  the  amount  of  damage  done.  It  often 
happens,  when  a crop  is  introduced  into  a new  locality,  that  insects 
previously  unknown,  finding  in  it  a desirable  food,  leave  their 
natural  food  plant,  multiply  rapidly  through  new  and  more  favor- 
able conditions,  and  thus  become  serious  pests.  This  is  what  has 
happened  to  shade-grown  tobacco  in  the  South.  The  suckfly  ( Dicy-:\ 
phus  minimus  Uhl.),  which  first  appeared  on  tobacco  in  1888,  has 
made  the  raising  of  a second  crop  of  shade-groAvn  tobacco  in  Florida 
unprofitable.  The  leaf  miner  or  splitworm  (F htliorimoea  operculella 
Zell.,  formerly  known  as  Gelechia  solanella  Boisd.)  also  has  at- 
tacked and  become  injurious  to  tobacco.  And  noAV  comes  a new  pest 
in  this  neAV  tobacco  thrips,  Avhich  has  threatened  to  surpass  the 
destructive  budworm  in  actual  injury. 

Injury  by  the  tobacco  thrips  Avas  first  observed  in  1902,  on  tobacco 
grown  in  the  field  on  which  the  first  shade  was  erected  in  1896. 
Since  that  time  the  insect  seems  to  have  increased  rapidly,  until, 
during  the  summer  of  1905,  the  thrips  Avas  found  in  all  shade  tobacco 
fields  examined,  and  the  opinion  is  expressed  by  several  planters  j 
that,  if  allowed  to  continue  its  ravages,  it  is  on  a fair  road  to  com-  ■ 
pletely  check  the  production  of  the  shade  crop. 

The  history  of  shade-grown  tobacco  in  this  country  dates  back  to 
the  year  1896,  when  one-fourth  of  an  acre  of  slat  shade  Avas  put  up  at  j 
Quincy,  Fla.  It  Avas  found  that  Sumatra  Avrapper  tobacco  grown  in 
this  AATay  nearly,  if  not  altogether,  equals  the  quality  of  the  imported 
article.  So  successful  has  been  the  raising  of  this  tobacco  that  to-day  j 
over  6,000  acres  are  grown  under  shade  in  Florida  and  the  adjoining 
counties  of  Georgia,  Avliile  Texas  has  a smaller  acreage. 

NATURE  AND  EXTENT  OF  INJURY. 

The  injury  occasioned  by  the  tobacco  thrips  is  known  as  u white  I 
vein,”  which,  as  the  term  indicates,  is  due  to  a Avhite  appearance  of 
the  veins  (see  PI.  I,  fig.  2).  These  veins  show  in  the  wrapper  when 
manufactured  into  cigars.  The  injury  is  brought  about  by  the  re- 
moval of  the  sap  by  the  adult  thrips  in  feeding  on  the  upper  surface  of 
the  leaf.  The  thrips  feed  on  the  space  between  the  veins  as  well  as 


Bui.  65,  Bureau  of  Entomology,  U.  S.  Dept,  of  Agriculture, 


Plate  I. 


Fig.  1 .—Slat-shade  Field,  Showing  Iron  Cowpeas  Grown  Between  Tobacco 
Crops.  (Original.) 


Fig.  2.— Leaf  of  Tobacco,  Showing  ‘White  Veins"  Caused  by  the  Tobacco 
Thrips  (Euthrips  nicotian/e).  (Original.) 


LIBRARY 

UNIVERSITY  OF  ILLINOIS 
URBANA 


ORIGIN  AND  DISTRIBUTION. 


( 

on  the  veins,  but  except  on  the  veins  themselves  the  indications  of 
their  feeding  disappear  in  the  fermentation  process. 

The  work  of  the  pest  should  not  be  confused  with  the  so-called 
u white  vein  ” that  sometimes  occurs  in  tobacco  grown  in  the  North 
and  which  seems  to  be  due  to  a physiological  disorder  of  the  plant. 

As  a result  of  the  th rips’s  work,  when  the  crop  is  affected  to  any 
extent,  all  the  white- vein  tobacco  must  be  sorted  into  a grade  by  itself 
and  sold  as  such,  the  expense  of  grading  being  thereby  largely  in- 
creased. The  value  of  the  crop  also  is  greatly  reduced,  as  there  is  no 
demand  for  this  grade  at  present.  There  seems  to  be  quite  a variation 
in  the  estimates  of  the  depreciation  of  tobacco  thus  affected,  one 
packer  estimating  the  value  as  decreased  from  $1.50  to  30  cents,  or 
a loss  of  $1.20  per  pound,  while  another  packer  places  the  decrease  at 
from  $1  to  50  cents,  or  a loss  of  50  cents  per  pound.  These  seem  to 
be  maximum  and  minimum  estimates. 

For  the  year  1904  it  is  estimated  that  20  per  cent  of  the  crop  grown 
under  slat  shade  was  damaged  to  such  an  extent  by  white  veins  that  it 
was  thrown  into  a grade  by  itself. 

The  injury  for  1905  was  decreased  to  a great  extent  by  the  heavy 
rainfall  in  the  latter  part  of  June  ail'd  in  July.  In  the  crop  of  tobacco 
sprayed  with  emulsion  there  were  practically  no  white  veins  to  be 
found,  and  this  was  the  case  in  1906.  Early  tobacco  was  especially 
affected  by  white  veins  in  1905,  the  injury  having  taken  place  pre- 
viously to  the  rains.  One  crop  of  tobacco  is  estimated  by  the  planter 
as  containing  33  per  cent  of  affected  wrappers,  practically  one-half 
of  which  must  necessarily  be  placed  in  a separate  grade.  Another 
crop  is  estimated  as  containing  20  per  cent  of  affected  wrappers,  10 
per  cent  being  placed  in  a separate  grade.  The  amount  of  injury  will 
vary  from  year  to  year,  depending  upon  the  period  and  amount  of 
rainfall.  ' 

In  the  past  the  greatest  damage  has  been  to  that  particular  section 
near  the  original  shade,  but  the  thrips  now  seem  to  be  disseminated 
throughout  all  the  fields  of  shade  tobacco. 

ORIGIN  AND  DISTRIBUTION. 

\ 

As  soon  as  possible  after  reaching  Quincy,  specimens  of  the  tobacco 
thrips  were  collected  and  sent  to  Dr.  W.  E.  Hinds,  an  authority  on 
this  group  of  insects.  He  found  that  they  represented  a new  species 
and  has 'named  and  described  them.® 

This  insect  was  taken  by  the  writer  at  Nacogdoches,  Tex.,  on  shade 
tobacco,  as  well  as  at  Quincy,  Fla.  In  April  adults  and  larvse  were 
taken  in  large  numbers  on  cocklebur  ( Xanthium  (jlabratum)  growing 
in  the  shade  fields  and  in  smaller  numbers  on  dewberry,  mustard,  and 
shepherd’s  purse  blossoms.  It  has  been  taken  by  the  writer  at  Dallas, 


® Proc.  Biol.  Soc.  Washington,  Yol.  XVIII,  pp.  197-199,  September,  1905. 


8 


THE  TOBACCO  THRIPS. 


Tex.,  in  both  winged  and  wingless  forms,  on  Johnson  grass  ( Sorghum  \ 
halepense)  in  March.  It  would  seem,  therefore,  to  be  a general 
feeder  and  widely  distributed  through  the  Southern  States. 

DESCRIPTION. 

Adult. — Doctor  Hinds  describes  the  adult  as  follows: 

Euthkips  nicotians  sp.  nov. 

Average  length,  1.05  mm.  (0.95  to  1.13  mm.)  ; average  breadth  at  middle  of 
abdomen,  0.27  mm.  (0.225  to  0.285  mm.).  General  color  of  head  and  thorax 
light  brown  or  tawny  yellow-brown ; abdomen  dark  brown. 

Head  about  one  and  one-half  times  as  wide  as  long,  frequently  slightly 

retracted  under  ante- 
rior margin  of  protho- 
rax ; occiput  trans- 
versely wrinkled,  pos- 
terior margin  strongly 
thickened  and  darker 
in  color ; anterior  mar- 
gin slightly  Insinuate, 
cheeks  approximately 
straight  and  parallel. 
Eyes  dark  red  in  col- 
or, not  protruding,  oc- 
cupying together  fully 
one-half  the  width  of 
the  front  of  the  head 
and  being  one  half 
long  as  the  head ; mar- 
gins around  eyes  pale 
yellow  in  color ; sur- 
face of  eyes  finely  fac- 
eted and  slightly  pi- 
lose; three  ocelli  present,  well  separated,  posterior  ones  contiguous  with  yellow 
borders  to  eyes,  pale  yellow  in  color  and  margined  inwardly  with  pale-orange 
crescents ; one  moderately  stout  dark  spine  in  front  of  each  posterior  ocellus ; 
postocular  spines  weak  and  inconspicuous.  Mouth  cone  reaching  nearly  to  pos- 
terior edge  of  the  prosternum,  tapering  abruptly;  maxillary  palpi  slender,  three- 
segmented.  Antennae  inserted  slightly  below  front  margin,  approximate  at 
base,  about  two  and  one-half  times  as  long  as  the  head  and  approximately  equal 
to  breadth  of  mesothorax ; relative  length  of  segments : « 

1 2 3 4 5 0 7 8 

0.2  11.4  13.5  13.0  12.2  10.2  3.0  4.5 

Segment  1 is  rounded,  three-fourths  as  long  as  broad ; 2 is  as  broad  as  1 ; 
following  segments  about  three-fourths  as  thick;  segments  3 to  0 are  con- 
stricted at  bases,  becoming  more  stout  successively.  Color  of  segments  1 and 
2 uniform  light  brown ; 3 to  5 pale  yellow  at  bases,  shading  to  brown  at  outer 
ends,  each  succeeding  segment  from  3 to  0 becoming  darker  in  color;  0 to  8 are 

« The  number  of  the  segment  is  given  above  the  line  and  below  it  the  number 
of  spaces  covered  upon  an  eye-piece  micrometer  by  an  average  of  the  segments 
of  10  antenme. 


Fig.  1. — The  tobacco  thrips  (Euthrips  nicotians’.) : Adult  insect. 
Much  enlarged  (author’s  illustration). 


DESCRIPTION. 


9 


dark  brown.  Spines  upon  segments  2 to  5 are  of  medium  size,  but  not  very  con- 
spicuous. Color  of  bead  varying  from  gray-brown  to  yellow-brown. 

Prothorax  about  five-ninths  as  long  as  broad  and  slightly  longer  than  the 
head;  sides  rounded,  slightly  wider  at  hind  than  at  fore  angles;  one  stout  spine 
at  each  anterior,  and  two  stouter  spines  of  equal  size  at  each  posterior  angle ; 
anterior  marginal  pair  of  spines  about  one-half  as  long  as  those  at  front  angles ; 
usual  row  of  five  spines  on  each  side  of  hind  margin,  of  which  number  4 is 
equal  in  strength  to  those  on  the  front  margin.  Mesothorax  nearly  one  and 
one-third  times  as  wide  as  the  prothorax,  broadest  posteriorly,  sides  curving 
outward ; mesonotum  without  conspicuous  spines,  posterior  margin  forming  an 
obtuse  angle  in  middle.  Metathorax  slightly  narrower  than  mesothorax,  sides 
nearly  parallel,  broader  than  protliorax  at  posterior  edge;  metanotum  bears 
two  pairs  of  spines  at  front  edge,  the  inner  pair  being  as  strong  as  those  at 
front  angles  of  prothorax.  Wings  present  (probably  reduced  at  some  season  of 
year),  average  length  about  0.68  mm.,  not  reaching  to  the  tip  of  the  abdomen, 
breadth  equal  to  about  one-thirteenth  of  their  length ; fore  wing  has  two  longi- 
tudinal veins, v each  bearing  stout  spines  set  at  regular  intervals ; fore  wings 
shaded  ash  gray,  hind  wings  gray  only  along  basal  three-fourths  of  midvein ; 
spines  on  wing  veins  dark  brown  and  conspicuous ; costa  bears  19  to  24  spines ; 
fore  vein,  13  to  18 ; hind  vein,  10  to  12 ; scale,  5 ; interior  of  scale,  1 ; fringe  of 
hairs  on  costa  of  fore  wing  quite  heavy,  in  length  exceeding  the  breadth  of  the 
wing.  Legs  of  medium  length,  lighter  than  body  in  color,  pale  yellow,  shaded 
more  or  less  with  brown  on  upper  side  at  middle  of  femora  and  tibiae ; a pair 

of  stout  brown  spines  at  inside  of  tip  of  each  tibia,  small  brown  spines  scat- 

tered along  feipora  and  tibiae ; spines  standing  in  two  rows  on  inner  side  of 
hind  tibiae  are  weak  and  only  about  four  in  each  row. 

Abdomen  nearly  cylindrical  to  eighth  segment,  then  tapering  abruptly  to  an 
acute  tip ; color  uniformly  dark  brown ; a still  darker-colored  narrow  chitinous 
thickening  extends  across  dorsal  side  of  segments  2 to  8 near  anterior  edge. 
Three  or  four  quite  stout  and  rather  conspicuous  dark-brown  spines  stand  at 
each  side  of  dorsal  plates  on  2 to  8;  six  rather  prominent  spines  stand  in  a 

row  on  posterior  edge  of  ventral  plates  2 to  7 ; terminal  spines  stout  and 

prominent;  tenth  segment  split  open  along  dorsal  median  line. 

Described  from  10  females. 

Male  specimens  of  this  species  have  not  been  found. 

Three  cotypes  (three  slides)  deposited  in  the  U.  S.  National  Museum. 
Type  No.  8434,  U.S.N.M.  Three  cotypes  (three  slides)  deposited  at  the  Massa- 
chusetts Agricultural  College.  Four  cotypes  (two  slides)  retained. 

Habitat. — Quincy,  Fla. ; Nacogdoches,  Tex. ; Climax,  Ga. 

Wingless  females  appear  in  May  and  seem  to  predominate  by  the 
latter  part  of  that  month. 

This  species  may  be  readily  distinguished  from  Euthrips  tritici 
Fitch  by  its  color,  which  is  brown,  that  of  tritici  being  yellow.  Dif- 
ferences in  structure  by  whifch  the  species  may  be  readily  separated 
are  found  in  the  postocular  spines,  those  of  nicotiance  being  weak  and 
inconspicuous,  while  those  of  tritici  are  quite  prominent.  On  the 
wings  prominent  differences  are  found  in  the  number  of  spines  on 
the  veins,  the  costa  of  nicotiance  bearing  from  19  to  24,  the  fore  vein 
13  to  18,  and  the  hind  vein  10  to  12,  while  in  tritici  the  costa  bears 
from  26  to  28,  the  fore  vein  20  to  22,  and  the  hind  vein  15  to  18. 

Egg. — The  eggs  are  deposited  in  the  tissues  of  the  stem  and  leaves. 

Larva,  first  stage. — Length  about  0.23  mm. ; width  of  mesothorax  0.11  mm. 

24372— No.  65—07  m 2 


10 


THE  TOBACCO  THRIPS. 


General  shape  fusiform.  Color  of  posterior  part  of  thorax  and  entire  abdomen 
pale  yellow ; elsewhere  pearly  white.  Head  quadrate ; eyes  reddish.  Antennae 
0.15  mm.  in  length ; distinctly  four-segmented ; basal  segment  cylindrical, 
short;  second  ovate,  slightly  shorter  than  the  third;  third  slightly  conical, 
the  apex  joining  the  second ; fourth  fusiform,  widest  near  the  basal  fourth, 
about  equal  in  length  to  the  other  three.  The  fourth  segment  is  distinctly 
annulated,  the  second  and  third  indistinctly  so;  setae  are  present  on  all  seg- 
ments, most  numerous  on  the  fourth.  Legs  translucent  white,  stout.  Abdomen 
tapering  posteriorly ; with  ten  segments,  the  first  eight  nearly  equal  in  length, 
the  ninth  twice  and  tenth  three  times  the  length  of  the  preceding.  Each 
abdominal  segment  with  longitudinal  rows  of  setae,  the  ninth  with  two  and 
tenth  with  four  spines  that  are  four  times  the  length  of  the  setae. 

Larva,  second  stage. — Length  from  0.6  to  1.17  mm. ; width  of  mesothorax  from 
0.14  to  0.2  mm. ; shape  same  as  in  first  stage.  Color  of  thorax  and  abdomen 
yellowish,  with  exception  of  the  last  abdominal  segment.  Head  quadrate ; 
antennae  with  four  segments,  the  fourth  being  more  distinctly  annulated  than  in 
the  first  stage.  Abdomen  with  the  setae  increasing  in  length  posteriorly;  ninth 
and  tenth  segments  about  equal  in  length,  each  less  than  twice  the  length  of  the 
others. 

The  young  nympli  or  prepupa. — Length,  0.52  to  0.62  mm. ; width  of  meso- 
thorax, 0.10  to  0.12  mm.  Antennae  translucent,  extending  forward,  much  short- 
ened and  composed  of  five  segments,  first  two  cylindrical  and  very  short,  third 
and  fourth  globose,  fifth  tapering  to  the  apex.  The  last  segment  of  the  abdomen 
is  set  with  four  spines  by  use  of  which  the  young  nymph  seems  to  protect  itself, 
when  approached  by  another  the  abdomen  being  turned  upon  it.  The  wing 
sheaths  are  very  noticeably  separated,  the  upper  one  extending  to  the  middle  of 
the  second  segment,  the  lower  one  to  the  middle  of  the  third  segment.  The  legs 
are  translucent  white,  stout. 

The  full-grown  nymph  or  pupa. — Length,  0.68  to  1.22  mm. ; width  of  meso- 
thorax, 0.15  to  0.20  mm.  Shape  similar  to  the  adult.  Color  yellowish;  head, 
antennae,  wing  pads,  legs,  and  caudal  segments  of  the  abdomen  varying  to  pearly 
white.  Antennae  extending  to  the  middle  of  the  prothorax.  Three  yellowish 
ocelli  between  the  eyes,  the  latter  dark  red.  Wing  pads  so  closely  applied  as  to 
appear  single,  extending  to  the  middle  of  the  fifth  abdominal  segment;  length 
from  head  to  tip  of  wing  pads  0.39  mm.  The  abdomen  is  noticeably  contracted 
longitudinally ; greatest  width,  0.24  mm. ; longest  setae,  0.078  mm. 

HABITS. 

Feeding. — When  examinations  were  first  made,  April  17,  the  adult 
thrips  were  found  feeding  in  the  seed  beds  on  the  upper  surface  of 
the  young  tobacco  plants,  and  in  the  field  on  the  upper  surface  of  the 
leaves  of  young  cocklebur  weeds.  In  the  larval  stage  they  feed  on  the 
lower  surface  of  the  leaves  of  tobacco  and  weeds,  but  as  they  become 
adult  seem  to  prefer  the  upper  surface,  a habit  which  is  very,  favorable 
for  remedial  treatment,  as  they  can  then  be  reached  much  more  readily 
by  sprays.  To  determine  the  attractiveness  of  tobacco  the  experiment 
was  tried  of  transplanting  young  tobacco  plants  into  a field  that  had 
been  prepared  ready  for  transplanting,  but  in  which  weeds,  consisting 
of  cockleburs  and  grass,  were  to  be  found. 

In  order  that  thrips  might  not  be  accidentally  taken  from  the  seed 
bed  on  the  plants,  the  latter  were  dipped  in  a solution  of  kerosene 
emulsion  and  this  washed  off  with  water.  Fifteen  plants  were  set  in 


LIFE  HISTORY. 


11 


a 2-acre  field  at  intervals  of  4 and  8 rods.  The  day  following  was 
rainy  and  unfavorable  to  movement  of  the  thrips,  but  the  second  fol- 
lowing day  was  pleasant.  In  the  afternoon  of  the  second  day  an 
examination  was  made,  and  four  plants  were  found  to  have  been  cov- 
ered with  dirt  in  the  ridging  for  setting  the  field.  Of  the  eleven 
remaining,  four  plants  were  found  without  thrips,  five  with  one  each, 
one  with  two,  and  one  with  three.  From  this  it  would  seem  that  the 
thrips  are  quite  strongly  attracted  from  the  weeds  in  the  field  to  the 
tobacco. 

As  the  thrips  commence  feeding  and  breeding  on  the  young  plants 
the  lower  or  sand  leaves  receive  the  greatest  amount  of  injury.  From 
the  lower  leaves  they  gradually  work  up  the  stalks  to  the  leaves  above, 
until  at  harvesting  time  they  have  reached  more  than  half  way  up. 
In  attacking  a leaf  they  first  appear  feeding  near  the  tip,  and  grad- 
ually work  toward  the  stem.  It  may  be  well  to  note  here  that  the 
leaves  are  harvested  by  picking — called  “ priming  ” — as  they  ripen, 
and  that  the  stalks  often  reach  the  slats  or  cloth  9 feet  from  the 
ground.  In  the  early  stages  of  the  tobacco  the  thrips  are  found  on 
that  grown  in  sun  and  shade  alike,  but  as  the  sun  tobacco  thickens 
up  they  seem  to  leave  it  and  are  found  in  numbers  only  on  the  shade- 
grown  tobacco.  In  a field  in  which  Cuba  and  Sumatra  varieties 
were  grown  together  the  thrips  were  found  to  be  equally  injurious  to 
both. 

Jumping. — When  disturbed,  the  adults  have  the  habit  of  jumping, 
and  have  thus  been  mistaken  by  some  for  small  fleas.  This  charac- 
teristic is  typical  of  the  genus  to  which  the  tobacco  thrips  belongs. 
The  motion  seems  to  be  produced  by  a combined  movement  of  the 
wings  and  abdomen. 

Flight. — The  closely  related  wheat  thrips  takes  flight  readily,  but 
the  tobacco  thrips  apparently  does  not  do  so.  Notwithstanding  all 
the  observations  he  has  made,  the  writer  has  as  yet  failed  to  see  it 
take  wing,  and  its  power  of  flight  must  be  limited. 

FOOD  PLANTS. 

The  tobacco  thrips  seems  to  be  a general  feeder,  as  adults  were  taken 
in  April  on  blooms  of  dewberry  ( Rubus  sp.),  shepherd’s  purse 
( Bursa  bursa-pastoris) , and  mustard  ( Brassica  sp.).  Adults  and 
larvae  were  taken  on  oats,  wheat,  and  cocklebur  as  well  as  on  tobacco. 

LIFE  HISTORY. 

Methods  of  study. — In  order  to  determine  the  life  cycle,  adult 
thrips  were  confined  in  small  wide-mouth  vials  on  parts  of  tobacco 
leaves  for  periods  of  twelve  and  twenty-four  hours,  but  repeated 
attempts  failed  to  induce  them  to  oviposit.  The  parts  of  tobacco 
leaves  were  thereupon  replaced  by  small  bean  pods,  with  the  result 
that  oviposition  soon  took  place.  Absorbent  cotton  was  used  as  a 
stopper  for  the  vial  in  order  to  keep  the  moisture  from  forming  on 


12 


THE  TOBACCO  THRIPS. 


the  inside  and  thus  catching  the  young  thrips,  which  readily  succumb 
when  so  caught. 

Life  cycle. — The  life  cycle  of  this  species  is  found  to  be  quite  short 
and  very  similar  to  that  of  the  closely  related  wheat  thrips,  Euthrips 
tritici.  In  May  and  June  only  twelve  or  thirteen  days  are  required 
for  its  completion.  In  the  tobacco  field  the  eggs  appear  to  be  depos- 
ited in  the  tissues  on  the  under  surface  of  the  leaf.  In  May  and  June 
the  incubation  period  for  eggs  laid  in  confinement  in  young  bean 
pods  seems  to  average  about  four  days.  The  larvse,  upon  hatching, 
feed  on  the  under  surface  of  the  leaf;  during  this  stage,  which  lasts 
seven  days,  and  before  changing  to  pupse,  they  molt  twice.  When 
about  to  pupate  the  larvae  crawl  to  some  obscure  nook;  there  they 
remain  inactive,  without  feeding,  during  the  pupal  stage,  which  lasts 
two  days.  The  adults,  on  emerging,  have  a yellowish  color,  which 
in  a few  hours  turns  to  the  normal  brown.  As  adults  the  thrips  crawl 
to  the  upper  surface  of  the  leaf  and  commence  feeding. 

Hibernation. — The  tobacco  thrips  appears  to  hibernate  in  the  adult 
stage.  When  the  fields  were  visited,  the  latter  part  of  October,  not  a 
specimen  could  be  found,  although  another  thrips  ( Chirothrips 
crassus  Hinds),  which  was  taken  in  large  numbers  in  sheaths  of 
grass  found  growing  in  the  tobacco  fields,  was  at  first  mistaken  for 
the  tobacco  thrips.  Mr.  W.  W.  Cobey  informed  the  writer  that  he 
had  observed  the  tobacco  thrips  on  the  leaves  of  cocklebur  about 
October  10,  previous  to  a cold  spell.  Thus  it  would  seem  that  the 
thrips  goes  into  hibernation  after  the  first  approach  of  cold  weather. 

OTHER  THRIPS  THAT  MAY  BE  MISTAKEN  FOR  THE  TOBACCO 

THRIPS. 

While  the  tobacco  thrips  is  the  only  species  commonly  found  on 
tobacco,  yet  a number  of  other  thrips  which  may  be  mistaken  for  this 
pest  are  found  in  the  vicinity  of  the  tobacco  fields,  or  even  acci- 
dentally upon  the  tobacco  itself.  Among  those  that  may  be  so  mis- 
taken are  the  following  species : 

Euthrips  tritici  Fitch,  the  “ wheat  thrips,”  is  a species  generally 
distributed  throughout  the  South.  It  has  a wide  range  of  food  plants 
and  can  be  found  during  a large  part  of  the  year  in  almost  any  blos- 
som. In  Florida  it  has  been  reported  as  injuring  the  orange  and 
strawberry  by  attacking  the  blossoms.  At  Quincy,  Fla.,  during  the 
summer  of  1905,  it  was  found  in  large  numbers  associated  with  the 
tobacco  thrips  in  oat  fields  bordering  the  tobacco  fields.  It  was  also 
found  seriously  injuring  roses,  causing  the  outer  petals  to  wither 
before  the  flowers  opened.  It  may  be  distinguished  from  the  tobacco 
thrips  by  the  yellowish  color  of  the  adult  or  winged  form,  which  in 
the  tobacco  thrips  is  dark  brown. 

Thrips  tabaci  Lind.,  the  “ onion  thrips,”  has  been  reported  by  Prof. 
A.  L.  Quaintance  as  quite  abundant  in  Florida,  attacking  onions, 


NATURAL  CONTROL. 


13 


cabbage,  and  cauliflower.  It  may  be  distinguished  from  the  tobacco 
thrips  by  its  color,  which  is  yellowish. 

Anthothrips  niger  Osborn  is  another  species  which  was  very  abun- 
dant at  Quincy  the  summer  of  1905.  In  oats  and  wheat  bordering 
the  tobacco  fields  it  was  found  breeding  in  vast  numbers  with  the 
wheat  and  tobacco  thrips.  It  was  also  occasionally  taken  on  tobacco 
and  tomato.  It  is  a strong  flyer,  and  may  be  further  distinguished 
from  the  tobacco  thrips  by  its  much  larger  size  and  black  color. 

A few  specimens  of  iMolothrips  bicolor  Hinds  were  taken  on  oats 
and  wheat  in  the  vicinity  of  tobacco  fields.  This  species  may  be 
distinguished  by  the  white  or  yellowish  pigmentation  of  the  first 
three  .segments  of  the  abdomen. 

C hirothrips  crassus  Hinds  was  taken  in  October  and-  November  in 
large  numbers  in  the  sheaths  of  grass  growing  in  tobacco  fields.  It 
was  at  first  mistaken  for  the  tobacco  pest,  because  of  the  similarity 
in  color,  but  may  be  easily  distinguished,  as  it  does  not  have  the 
jumping  habit  of  the  tobacco  thrips. 

NATURAL  CONTROL. 

Rains . — Of  the  natural  checks,  rain  is  the  most  important.  It  is 
known  that  nearly  all  thrips  thrive  during  warm  and  dry  weather, 
and  that  they  are  washed  from  their  food  plants  and  destroyed  in 
numbers  by  rain.  This  is  true  of  the  tobacco  thrips  in  that  it  is 
washed  off  by  heavy  rains,  yet  unless  the  rain  continues  for  several 
days  few  seem  to  be  destroyed,  for  at  the  end  of  the  first  or  by  the 
second  clear  day  following  the  writer  has  found  it  on  the  leaves  in  as 
large  numbers  as  ever. 

The  influence  of  rain  upon  the  pest,,  however,  was  very  noticeable  in 
its  effect  during  the  summer  of  1905.  Up  to  the  latter  part  of  June 
very  little  rain  had  fallen,  and  the  drought  was  showing  its  effect  on 
the  unirrigated  fields.  At  this  time  the  dry  spell  was  broken  and 
rains  were  heavy  and  frequent.  The  June,  1905,  rainfall,  which  was 
nearly  three  times  that  of  the  preceding  June,  yet  still  below  the  nor- 
mal, nearly  all  fell  during  the  latter  part  of  the  month  and  was  fol- 
lowed by  the  heavy  July  rainfall,  which  was  the  greatest  since  1900, 
and  more  than  twice  that  of  1904.  As  a result  the  thrips  were  kept  off 
the  leaves,  the  plants  grew  rapidly,  and  priming  was  forced  into 
twenty  days  where  it  usually  takes  thirty.  The  sand  leaves  were  lost 
in  large  part  because  of  this  rapid  ripening  and  the  leaves  affected  to 
the  greatest  extent  by  white  vein  were  thus  eliminated  from  the  crop. 
As  the  result  of  these  weather  conditions,  white  veins  in  the  late  to- 
bacco were  reduced  to  a very  small  percentage. 

The  great  amount  of  injury  in  1904  was  undoubtedly  due  to  the 
exceptionally  droughty  season.  This  will  be  shown  by  the  accom- 
panying chart  (fig.  2)  of  total  monthly  precipitation  for  the  last 
seven  years.  That  during  1905  and  1900  the  injury  was  so  much 


14 


THE  TOBACCO  THRIPS. 


less  than  in  1904  must  have  been  due  to  the  greater  precipitation. 
As  before  stated,  it  is  quite  evident  that  the  amount  of  injury  by 
thrips  will  vary  from  year  to  year,  depending  upon  the  period  and 
amount  of  rainfall.  The  total  precipitation  in  inches  at  Tallahassee, 
Fla.,  during  April,  May,  June,  and  July  of  the  years  1898-1906  is 
shown  in  the  following  table : 


Precipitation  in  inches  at  Tallahassee. 


April. 

May. 

June. 

July. 

Length  of 
record 
(years). 

Year. 

Total. 

Depar- 
ture from 
normal. 

Total. 

Depar- 
ture from 
normal. 

Total. 

Depar- 
ture from 
normal. 

Total. 

Depar- 
ture from 
normal. 

1898 

0. 87 

-1.89 

1.55 

-2. 65 

4.49 

- 1.25 

10. 00 

+ 1.71 

14 

1899 

1900 

4.05 

4-1. 05 
— 0. 27 

2.06 

-1.60 

16.47 

+10. 72 

10.31 

+1.87 
+0. 02 
-2.  40 

15 

1901 

2. 72 

5. 07 

+1.59 

—0.62 

5. 61 

- 0.75 

8.25 

16 

1902 

0.84 

-1.15 

2.  86 

9. 94 

+ 3.58 

5. 83 

17 

1903 

0.11 

—1. 88 

5.59 

+2. 11 

10. 01 

+ 3.65 

7.09 

—1.14 

18 

1904  

1.65 

-0. 34 

1.05 

-2.43 

1.33 

- 5.03 

3. 95 

. -4.28 

19 

1905 

0.  92 

—1.07 

7.55 

+4.  07 

3. 50 

- 2.86 

8. 76 

+0.53 

20 

1906 

0. 15 

-2. 43 

2.92 

+0. 70 

5. 17 

- 1.23 

8.88 

+1.00 

21 

Insects. — Specimens  of  a small  bug,  Triphleps  insidiosus  Say, 
were  found  very  commonly  upon  oats,  where  they  seemed  to  be  quite 
destructive  to  the  thrips.  When  captured  with  the  thrips  by  sweep- 
ing the  oats  with  a net,  they  were  shortly  found  with  a thrips  im- 
paled upon  their  beaks,  sucking  out  the  juices.  While  this  insect 
may  assist  in  decreasing  the  tobacco  thrips  that  breed  on  oats,  it  has 
not  as  yet  been  found  on  tobacco. 

A fungus  also  was  found  growing  upon  dead  thrips  taken  from 
tobacco  in  the  seed  bed;  but  this  may  be,  and  probably  is,  a form 
attacking  the  insect  after  its  natural  death. 

REMEDIES. 

Remedies  may  be  considered  under  two  heads,  namely,  cultural 
methods  and  insecticide  applications. 

CULTURAL  METHODS. 

It  is  the  practice  of  many  tobacco  growers  to  start  the  seed  bed  in 
the  shade-tobacco  field  (see  PI.  II),  and,  after  the  plants  are  removed, 
to  plant  it  with  the  rest  of  the  field.  This  practice  is  unquestionably 
a bad  one,  not  alone  from  its  furnishing  a breeding  place  for  the 
thrips,  but  also  because  it  becomes  a center  of  infestation  for  many 
other  pests,  particularly  flea -beetles.  It  was  noticed  during  the  sum- 
mer of  1905  that  insect  pests,  and  especially  flea-beetles,  were  the  most 
numerous  in  transplanted  seed  beds  and  in  that  part  of  the  field 
adjoining  the  seed  bed.  It  seems  advisable,  therefore,  that  the  seed 
bed  be  located  oqtside  and  at  some  distance  from  the  tobacco  field. 
Where  it  is  necessary  that  the  seed  bed  be  located  in  the  field,  the 
thrips  can  be  largely  overcome  by  frequent  applications  of  kerosene 
emulsion,  as  hereinafter  described.  Applications  of  Paris  green  also 


CULTURAL  METHODS. 


15 


Fig.  2. — Diagram  showing  total  monthly  precipitation  at  Tallahassee.  Fla.,  during  April, 
May,  June,  and  July,  1900-1906,  to  illustrate  relation  of  rainfall  to  amount  of  injury 
by  the  tobacco  thrips,  (Original.) 


16 


THE  TOBACCO  THRIPS. 


should  be  made  to  check  other  insects.  This  will  apply  to  the  seed 
bed  wherever  it  be  located. 

Since  it  is  evident  that  the  thrips  pass  the  period  between  crops 
in  the  tobacco  field  feeding  upon  catch  crops  that  follow,  as  rye, 
wheat,  etc.,  or  upon  weeds  which  have  been  allowed  to  grow,  it  seems 
advisable  that  thorough  and  clean  cultivation  be  practiced.  While 
it  is  possible  that  the  employment  of  the  kerosene  emulsion  treat- 
ment, as  recommended,  may  prove  so  effective  as  to  permit  the  grow- 
ing of  catch  crops  (PL  I,  fig.  1)  without  injurious  effect,  yet  a thor- 
ough cultivation  of  the  soil  after  the  crop  is  harvested  is  strongly  j 
advised,  for  besides  its  effect  on  the  thrips  it  will  result  in  the  destruc- 
tion of  budworm  and  hornworm  pupae  and  grasshopper  eggs. 

As  soon  as  priming  is  finished  the  stalks  should  be  plowed  under, 
together  with  all  other  vegetation  in  the  field.  Although  cockleburs 
were  observed  repeatedly  during  the  summer  of  1905,  coming  up  the 
day  following  cultivation,  and  although  the  seed  may  lie  in  the  soil 
two  and  three  years  before  germinating,  yet  if  the  weeds  are  prevented 
from  fruiting  in  the  fall  by  keeping  the  soil  well  plowed  the  effect 
will  soon  become  apparent. 

The  practice  followed  by  some  planters  of  keeping  a space  of  10 
feet  bordering  the  shade  field  free  from  all  vegetation  is  quite  desira- 
ble as  affecting  the  thrips. 

It  is  the  general  practice  to  grow  oats  in  fields  bordering  the  shade 
tobacco,  but  as  the  tobacco  thrips  is  found  breeding  in  vast  numbers 
in  oats  it  would  seem  advisable  to  replace  oats  with  corn  in  these 
border  fields. 

The  part  that  irrigation  may  take  in  controlling  the  thrips  seems 
to  be  of  importance.  Somewhat  less  than  one-fourth  of  the  shade 
tobacco  in  Florida  is  irrigated.  This  is  carried  out  by  one  of  two 
methods,  namely,  surface  or  overhead  delivery.  Surface  irrigation, 
which  is  largely  practiced,  does  not  seem  to  affect  the  pest.  In  the 
overhead  method  piping  is  employed,  provided  at  intervals  with 
lateral^  that  extend  4 or  5 feet  above  the  cover  and  to  which  are 
attached  nozzles  that  give  a fountain  spray.  In  this  way  an  artificial 
rain  is  produced.  This  overhead  irrigation  seems  to  have  quite  a 
noticeable  effect  in  decreasing  the  numbers  of  thrips.  Three  irriga- 
tions weekly  seem  to  be  much  more  effective  than  two.  One  firm 
estimates  a decrease  in  injury  of  10  per  cent  in  a field  thus  irrigated  , 
in  1904.  The  great  expense  of  piping  and  damage  from  freezing  has 
kept  the  method  from  being  installed  to  any  great  extent  as  yet. 

In  growing  wrapper  tobacco,  shade  is  produced  by  the  use  of  either 
slats  (PI.  I,  fig.  1;  PI.  II,  fig.  1)  or  cheese  cloth.  (PI.  IT,  fig.  2.) 
The  temperature  in  the  shade  produced  by  the  former  is  reduced 
about  10°  from  the  normal,  while  by  the  latter  it  is  increased  10°. 
From  information  received  it  is  found  that  the  thrips  have,  up 


Bui.  65,  Bureau  of  Entomology,  U.  S.  Dept,  of  Agriculture. 


Plate  II. 


Fig.  1 .—Slat-shade  Tobacco  Field,  Showing  Seed  Bed.  (Original.) 


Fig.  2.— Cheesecloth-shade  Tobacco  Field,  Showing  Seed  Bed.  (Original.) 


n 


library 

RSITY  Of  ILLINOIS 

URBANA 


INSECTICIDES. 


17 


to  the  present  time,  caused  a much  larger  percentage  of  injury  to 
tobacco  grown  under  the  slat  shade.  During  the  summer  of  1905, 
however,  they  were  found  causing  no  small  amount  of  injury  to 
tobacco  under  cheese  cloth.  Whether  or  not  the  meteorological  dif- 
ferences between  cheese-cloth  and  slat  shade  have  an  influence  on 
the  thrips’s  work,  can  not  be  told  at  present,  but  the  matter  is  im- 
portant and  should  be  watched  closely. 

INSECTICIDES. 

Tn  carrying  on  experiments  to  determine  the  most  effective  and 
practical  insecticides,  reference  was  made  to  Professor  Quaintance’s 
bulletin  entitled  “ The  Strawberry  and  the  Onion  Thrips.”  a The 
insecticides  which  Professor  Quaintance  found  to  be  most  effective 
on  Euthrips  tritici  were  given  repeated  trials.  As  a result  it  was 
found  that  the  resistance  of  the  tobacco  thrips  to  insecticides  is  far 
greater  than  that  of  Euthrips  tritici. 

In  experimenting  with  insecticides  three  important  points,  aside 
from  their  effect  upon  the  insect,  were  to  be  considered:  First,  their 
relative  cost;  second,  the  expense  involved  in  their  application;  and, 
third,  their  effect,  if  any,  upon  the  foliage.  From  the  nature  of  the 
mouth  parts  of  thrips,  which  are  fitted  Tor  piercing  and  sucking, 
stomach  poisons  were  not  available  and  contact  insecticides  were 
necessarily  used.  These  latter,  as  is  generally  known,  kill  by  entering 
through  the  breathing  pores  and  setting  up  an  irritation,  or  by  closing 
them  and  bringing  about  the  death  of  the  insect  from  suffocation.  It 
has  been  found  that  the  adult  feeds  largely  on  the  upper  surface  of  the 
leaves.  In  this  habit,  therefore,  lies  our  opportunity  to  treat  the 
pest  successfully  with  insecticides. 

Among  the  insecticides  experimented  with  are  the  following, 
the  sprays  being  applied  with  a knapsack  sprayer : 

Rose-leaf  insecticide. — This  is  a high-grade  extract  of  tobacco. 
Professor  Quaintance,  in  his  experiments  with  the  wheat  thrips, 
finds  this  insecticide  to  be  the  most  effective  and  practical  remedy 
for  use  against  the  thrips  affecting  strawberries,  and  recommends 
for  that  species  1 part  to  48  of  water.  This  strength,  when  used 
upon  the  tobacco  thrips,  has  but  little  effect.  Various  strengths 
were  tried.  When  1 part  of  the  insecticide  to  20  parts  of  water  is 
used,  the  thrips  seem  to  be  paralyzed,  remaining  immovable  for 
about  an  hour  and  a half,  after  which  they  commence  to  show  life, 
and  soon  become  as  active  as  ever.  Further  experiments  with  this 
insecticide  show  it  to  be  effective  when  used  with  whale-oil  soap  in 


the  following  proportions: 

Rose-leaf  insecticide-  1 quart. 

Whale-oil  soap ^ \ pound. 

Water -<>  quarts. 


« But  46,  Fla.  Agric.  Exp.  Sta.,  July.  1803. 


18 


THE  TOBACCO  THRIPS. 


Nikoteen. — This  is  a preparation  advertised  as  containing  40  per 
cent  of  nicotine.  It  was  applied  in  various  strengths.  Sprayed  at 
the  rate  of  1 part  to  144  of  water,  38  per  cent  of  the  thrips  were  found 
to  be  dead  when  the  examination  was  made,  twenty- four  hours  later. 
No  greater  strengths  were  tried,  as  the  cost  of  the  insecticide  would 
not  allow  its  use. 

Tobacco  decoction. — This  was  made  by  boiling  1 pound  of  tobacco, 
stems  and  leaves,  in  1 gallon  of  water  for  a half  hour.  This  strength 
was  very  effective,  practically  all  of  the  thrips  that  were  fairly  hit 
by  the  spray  being  killed.  Weaker  strengths  were  less  efficient.  As 
other  forms  of  nicotine  were  found  to  be  more  effective  in  combination 
with'  whale-oil  soap,  the  latter  was  used  with  the  decoction.  When 
so  used,  however,  the  mixture,  owing  apparently  to  some  chemical 
change  which  had  taken  place,  burned  the  leaf. 

Whale-oil  soap. — This  was  used  in  the  proportion  of  1 pound  of 
soap  to  6 gallons  of  water.  When  examined  shortly  after  spraying 
the  thrips  were  seemingly  as  lively  as  ever.  A strength  of  1 pound 
to  5 gallons  killed  about  50  per  cent  of  the  thrips,  but  seemed  to 
burn  the  leaf  slightly. 

Glucose  and  molasses. — It  was  thought  that  possibly  the  thrips 
might  be  caught  or  prevented  from  working  on  the  leaf  by  means  of 
a sticky  spray.  A proportion  of  1 quart  of  glucose  to  6 quarts  of 
Avater  was  tried.  While  a feAV  thrips  Avere  caught  and  killed  by  the 
spray,  others  had  escaped  and  Avere  found,  after  the  water  had  eA^apo- 
rated,  Avalking  about  OA^er  the  leaf  without  trouble.  Molasses,  also, 
Avas  tried,  but  found  to  be  even  less  effective  than  the  glucose. 

Dusting  with  lime  or  other  poAvders  seems  to  be  of  little  A^alue,  as 
the  thrips  are  found  making  their  Avay  about  through  the  dust  with- 
out trouble.  Lime  also  has  the  disadvantage  that  it  is  not  entirely 
Avashed  off  by  rains. 

Arsenicals  were  tried,  but,  as  expected,  seem  to  be  of  little  value 
Avhen  used  for  the  thrips. 

Kerosene  emulsion. — Since  this  is  our  strongest  contact  poison  it 
Avas  thought  from  the  first  that  if  it  could  be  used  in  sufficient  strength 
to  kill  the  thrips  Avithout  injury  to  the  tobacco  leaf,  it  would  furnish 
a satisfactory  remedy.  Experiments  Avere  made  with  the  folloAving 
formula  for  the  stock  solution : 

Kerosene - gallons. 

Hard  soap - £ pound. 

Water __  1 gallon. 

A strength  of  1 part  of  stock  solution  to  10  parts  of  Avater  proved 
quite  satisfactory  in  killing  the  thrips.  This  spray  was  found  to 
burn  the  leaves  when  used  in  the  sun,  but  further  experiments  have 
demonstrated  that  it  can  be  used  on  a cloudy  day  or  late  in  the  evening 
Avithout  danger  of  injury. 


WHEN  TO  APPLY  KEROSENE  EMULSION. 


19 


THE  BEST  TREATMENT. 

Of  the  many  insecticides  used,  kerosene  emulsion  has  been  found 
to  be  the  most  satisfactory  remedy  for  the  tobacco  tlirips.  Tobacco 
decoction  in  a concentrated  strength  seems  to  be  effective,  but,  because 
of  the  amount  of  material  necessary  and  the  labor  involved  in  its  prep- 
aration, its  use  is  less  satisfactory.  Rose-leaf  insecticide,  while  effect- 
ive in  concentrated  strengths,  is  impractical  because  of  its  greater 
expense  as  compared  with  the  emulsion.  The  advantages  of  kerosene 
emulsion  are  its  destructive  power  against  the  insects  and  its  low  cost 
when  compared  with  other  possible  remedies.  Its  one  disadvantage 
lies  in  the  fact  that  it  can  not  be  applied  while  the  sun  is  shining. 
This  has  been  overcome  by  night  applications,  as  herein  described. 

It  was  suggested  that  the  kerosene  might  affect  the  aroma  of  the 
cigar.  Cigars  wrapped  with  sprayed  tobacco,  however,  fail  to  give 
evidence  of  any  such  effect.  Very  particular  attention  was  paid  to 
this  point,  but  no  traces  whatever  of  the  kerosene  in  either  the  leaf  or 
the  cigar  could  be  detected. 

HOW  TO  MAKE  KEROSENE  EMULSION. 

The  formula  heretofore  given,  namely,  2 gallons  of  kerosene,  1 gal- 
lon water,  and  one-half  pound  of  soap,  is  followed  when  hard  soap 
is  used.  The  soap  should  be  cut  into  fine  shavings  and  dissolved  in 
the  gallon  of  boiling  water.  The  water  should  then  be  added  to  the 
kerosene  while  still  hot  and  churned  by  means  of  a force  pump,  pump- 
ing it  back  into  the  same  vessel  for  ten  minutes.  When  thoroughly 
emulsified  it  has  a creamy  appearance  and  upon  cooling  becomes  much 
thicker. 

A certain  naphtha  soft  soap  is  now  manufactured  that  will  dis- 
solve readily  and  by  the  use  of  which  the  emulsion  can  be  made  with- 
out heat.  When  this  soap  is  used,  a pint  will  replace  the  hard  soap 
in  the  formula.  This  naphtha  soap  has  the  advantage  that  it  can  be 
made  up  at  short  notice  and  at  any  place  needed.  In  lots  of  100 
pounds  it  can  be  obtained  at  3J  cents  per  pound.  Whale-oil  soap  has 
been  used  to  replace  hard  soap  in  the  formula,  but  seems  to  have  very 
little  advantage  over  hard  soap. 

When  making  the  emulsion,  care  should  be  taken  that  it  is  com- 
pletely emulsified.  Each  particle  of  the  kerosene  must  be  surrounded 
by  a film  of  soap,  and  unless  this  be  brought  about  by  thorough 
churning  with  the  force  pump  the  kerosene,  being  free,  will  not  mix 
with  the  water,  but  will  rise  to  the  surface  and,  as  the  sprayer  be- 
comes nearly  empty,  will  be  forced  out  in  the  spray  and  burn  the 
foliage. 

WHEN  TO  APPLY  THE  EMULSION. 

The  emulsion  should  be  applied  first  when  the  plants  are  in  the 
seed  bed.  A number  of  applications  will  be  advisable  in  order  that 


20 


THE  TOBACCO  THRIPS. 


the  hibernated  thrips  may  be  killed  and  not  carried  to  the  field  on 
the  plants  when  set  out.  Spraying  in  the  field  should  be  commenced 
as  soon  as  the  plants  are  transplanted.  Two  applications  a week, 
when  possible,  seem  advisable.  By  starting  when  the  plants  are  in 
the  seed  bed  and  spraying  regularly,  it  seems  probable  that  the  pest 
can  be  almost  entirely  checked. 

In  combating  the  budworm  of  tobacco  it  is  necessary  to  apply  Paris 
green  in  the  leaf  bud  (1  tablespoonful  to  a peck  of  corn  meal)  two  or 
three  times  weekly  to  prevent  serious  injury.  The  moisture  fur- 
nished by  the  kerosene  spray,  when  it  comes  in  contact  with  the  Paris 
green,  has  a tendencj'  to  slightly  burn  the  bud,  and  care  should  be 
taken  not  to  spray  into  the  bud  more  than  is  necessary.  As  the  plants 
get  larger  this  can  be  easily  prevented.  Tt  will  be  found  well  to 
apply  the  Baris  green  and  meal  on  the  morning  following  the  spray- 
ing. when  possible. 

HOAV  TO  USE  THE  EMULSION. 

After  experimenting  with  different  strengths  it  was  found  that 
1 part  of  the  stock  emulsion  to  10  parts  of  water  is  effective.  The 
emulsion  may  be  handily  diluted  to  the  required  strength  in  large 
quantities,  in  barrels  or  casks  set  near  the  rows  to  be  sprayed.  If 
left  standing  for  longer  than  two  days,  the  kerosene  separates  from 
the  soap  and  therefore  should  not  be  diluted  until  the  day  it  is  to  be 
applied  or  day  before.  The  tobacco  has  been  sprayed  with  emulsion 
during  the  day  until  it  was  6 inches  high  without  burning.  Even 
if  burning  does  occur  in  this  early  stage  it  is  not  objectionable,  as 
the  leaves  drop  from  the  stalk  before  priming  commences. 

The  emulsion  is  best  applied  by  means  of  a knapsack  sprayer. 
While  the  plants  are  small  the  insecticide  can  be  properly  applied 
by  spraying  one  row  at  a time,  but  as  the  plants  get  larger  it  has  been 
found  best  to  spra}^  a row  twice,  going  down  on  one  side  and  back  on 
the  other.  It  has  been  found  that  spraying  can  be  commenced  shortly 
after  5 o’clock  in  the  evening,  except  it  be  a very  bright,  hot  day, 
when  it  will  be  necessary  to  wait  until  a little  later.  On  large  planta- 
tions this  gives  insufficient  time  during  daylight,  and  spraying  after 
dark  becomes  necessary.  In  so  spraying  after  dark  the  use  of  two 
hands  to  a row,  one  on  each  side,  preceded  by  a boy  with  a lantern  or 
a torch,  is  a very  satisfactory  and  economical  method  of  application. 
Care  should  be  taken  that  the  spray  is  distributed  over  all  the  leaves, 
as  it  must  come  in  contact  with  the  thrips  when  sprayed  in  order  to 
be  effective. 

COST  OF  SPRAYING. 

Supplies  and  labor. — The  applications  necessary  to  keep  the  pest 
in  check  will  be  found  to  vary  considerably,  depending  upon  the  rain- 
fall. It  seems  improbable  that*  spraying  for  the  maximum  period  of 
ten  weeks  will  be  found  necessary  when  regular  spraying  is  started 


CAUTION. 


21 


while  the  plants  are  still  in  the  seed  bed.  The  amount  of  spray  neces- 
sary and  the  labor  required  ip  spraying  varies  with  the  growth  of 
the  plant.  It  was  found  in  June,  when  the  plants  were  about  2 feet 
high,  that  8 acres  were  sprayed  in  four  hours  by  nine  men  and  three 
bo37s,  using  six  spray  pumps  and  applying  50  gallons  of  the  diluted 
emulsion  per  acre.  This  was  at  a cost  of  about  55  cents  an  acre  for 
labor  and  50  cents  for  spray.  It  is  roughly  estimated  that  the  ex- 
pense will  not  exceed  $20  an  acre,  even  if  found  necessary  to  spray 
twice  weekly  for  the  maximum  period  of  ten  weeks. 

Apparatus . — In  applying  the  emulsion  it  is  necessary,  from  the 
nature  of  the  crop,  to  use  a knapsack  sprayer.  These  sprayers  can 
be  purchased  for  from  $5  to  $15.  The  writer  would  recommend  the 
the  purchase  of  the  better  grades,  as  they  will  be  found  the  most 
satisfactory  and  in  the  end  the  cheapest. 


SUMMARY  OF  RECOMMENDATIONS. 

The  following  recommendations  are  made  as  a result  of  the  ex- 
periments carried  on  in  1905,  and  the  success  following  their  practice: 

1.  Practice  clean  cultivation  of  the  field  between  crops. 

2.  Plant  fields  bordering  the  shade  to  other  than  cereal  crops. 

fi.  Locate  the  seed  bed  outside  the  tobacco  field. 

4.  Apply  kerosene  emulsion  (1  part  to  10  parts  of  water)  with  a 
knapsack  sprayer  twice  a week  regularly,  commencing  while  the 
plants  are  in  the  seed  bed. 

It  is  very  important  that  the  spray  be  regularly  and  carefully  ap- 
plied during  the  first  few  weeks  after  transplanting,  in  order  that  the 
adult  thrips  which  have  passed  the  winter  in  the  tobacco  field  be 
killed  before  depositing  their  eggs  on  the  tobacco  or  weeds  in  the  field. 

CAUTION. 

The  kerosene  emulsion  must  be  churned  until  thoroughly  emulsi- 
fied, else  burning  will  follow  the  application. 

The  emulsion  should  not  be  made  up  to  the  1 to  10  strength  until 
shortly  before  using,  as  when  left  standing  for  longer  than  two  days 
the  excess  of  water  has  a tendency  to  dissolve  the  soap  surrounding 
rhe  oil  globules,  setting  the  oil  free. 

Spraying  must  be  done  in  the  evening  (after  5 o’clock),  else  the 
sun’s  rays  will  cause  a burning  of  the  leaves,  following  the  spray. 
Spraying  may  be  done  on  a cloudy  day,  but  only  when  there  is  no 
danger  of  the  clouds  breaking  away  and  allowing  the  sun  to  appear. 

Spraying  should  not  follow  an  application  of  Paris  green,  and 
when  preceding  it  the  plants  should  be  allowed  to  dry  before  the 
Paris  green  is  applied.  Care  should  be  taken  not  to  spray  into  the 
leaf  bud,  so  far  as  that  can  be  avoided. 


22 


THE  TOBACCO  THRIPS. 


ADDENDA. 

THE  TOBACCO  r£HRIPS  IN  1905-6. 

Although  the  writer  was  unable  to  continue  the  work  in  Florida 
the  past  year  (1906),  as  planned,  he  took  advantage,  in  November,  of 
the  opportunity  offered  to  visit  Quincy.  An  interview -with  several 
planters  was  sufficient  to  further  convince  him  of  the  practicabilit}^ 
of  spraying  with  the  kerosene  emulsion  and  the  efficiency  of  this  spray 
when  carefully  applied. 

The  injury  produced  by  the  thrips  the  past  year  has  been  only 
about  60  per  cent  of  that  of  1905.  This  is  undoubtedly  due  to  the 
variation  in  the  period  and  the  amount  of  precipitation,  as  before 
stated  by  the  writer. 

EFFECT  OF  THE  SPRAY. 

As  previously  stated,  the  writer  was  associated  during  the  work  on 
this  insect  with  Mr.  W.  W.  Cobey,  tobacco-breeding  expert  of  the 
Bureau  of  Plant  Industry.  During  the  past  two  years  Mr.  Cobey 
has  had  opportunity  to  observe  the  results  obtained  from  the  use 
of  the  kerosene-emulsion  spray  and  at  the  request  of  the  writer  has 
prepared  the  following  statement  in  relation  to  its  effect  on  the 
character  of  the  tobacco  and  the  desirability  of  its  use : 

It  is  the  opinion  of  the  writer,  after  a careful  comparative  study  of  the 
treated  and  untreated  tobacco,  that  the  use  of  kerosene  emulsion  on  tobacco, 
when  carefully  prepared  and  applied  at  the  proper  time  under  favorable  con- 
ditions, is  in  every  way  practicable  and  can  be  profitably  employed  by  tobacco 
growers  in  preventing  almost  wholly  the  ravages  of  this  insect.  There  was 
considerable  apprehension  among  the  tobacco  growers  at  first  regarding  the 
probable  injurious  effects  of  the  kerosene  emulsion  on  the  character  of  the 
tobacco.  However,  a careful  study  of  the  cured  and  fermented  tobacco  from 
the  sprayed  plants  showed  that  the  spraying  with  kerosene  emulsion  had  not 
injured  the  quality  or  reduced  the  value  of  the  crop.  It  has  been  impossible 
to  discover  any  difference  in  the  color,  elasticity,  or  aroma  of  the  treated  and 
untreated  tobacco  after  curing  and  fermenting.  On  the  other  hand,  the  pre- 
vention of  injury  to  the  tobacco  by  the  thrips,  by  means  of  the  kerosene-emul- 
sion spray,  prevented  a serious  loss  to  the  grower. 

The  injured  tobacco  may  be  fermented  sufficiently  to  even  up  the  color  of 
the  leaves  and  darken  the  white  or  discolored  veins  so  that  the  injury  will  not 
be  noticeable,  but  this  severe  sweating  will  darken  the  leaves  to  such  an 
extent  that  they  can  only  be  classed  as  dark  wrapper. 

The  use  of  the  spray  was  quite  general  during  the  season  of  1900,  and  seri- 
ous injury  to  the  tobacco  from  the  thrips  was  thus  prevented.  It  was  found 
by  those  who  commenced  to  apply  the  spray  early  in  the  season  and  were 
forced  to  discontinue  it  after  the  tobacco  was  about  2 feet  high,  that  there  was 
but  very  little  injury  by  the  thrips,  while  those  who  did  not  use  it  suffered  a loss 
to  an  extent  of  about  one-fourth  of  that  of  1904.  During  the  year  the  injury 
under  slat  shade  was  very  slight. 

For  those  who  may  apprehend  injury  to  the  quality  of  the  tobacco  it  may 
be  said  that  the  experiments  conducted  during  the  last  two  seasons  indicate 
that  when  spraying  is  begun  very  early  in  the  season  It  will  not  be  necessary 
to  continue  it  after  the  crop  is  about  half  grown. 


INDEX. 


Page. 

JEolothrips  bicolor , mistaken  for  tobaeco  thrips^-  _ 13 

Anthothrips  niger,  mistaken  for  tobaeco  tbrips 13 

Arsenicals,  ineffective  against  tobacco  thrips 18 

Brassica  sp.  (See  Mustard.) 

Bud  worm,  cultivation  as  remedy 1(3 

most  injurious  of  tobacco  insects  in  South  in  past  __  6 

Bursa  bursa-pastor  is.  (See  Shepherd’s  purse.) 

Cabbage,  food  plant  of  Thrips  tabaci . __  _ 12-13 

Cauliflower,  food  plant  of  Thrips  tabaci 12-13 

Chirothrips  crassus,  on  grass,  mistaken  for  tobacco  thrips 12, 13 

Cocldebur,  food  plant  of  tobacco  thrips 7,  11 

Cultivation,  remedy  for  tobacco  insects 1(3 

Dewberry,  food  plant  of  tobacco  thrips _ 7,11 

Dicyphus  minimus,  on  tobacco . __ 6 

Euthrips  nicotiance.  (See  also  Thrips,  tobacco.) 

description  of  adult  and  stages 8-10 

tritici,  mistaken  for  tobacco  thrips 5, 12 

Flea-beetles,  in  tobacco  fields 14 

Fungus,  found  on  dead  tobacco  thrips 14 

Gelechia  solanella=Phthorima,a  operculella (3 

Glucose  and  water,  ineffective  against  tobacco  thrips 18 

Grass,  food  plant  of  Chirothrips  crassus 32,  13 

Grasshoppers,  cultivation  as  remedy 16 

Hornworm,  cultivation  as  remedy 16 

Insect  enemies  of  tobacco 6 

thrips 14 

Insecticides,  used  in  experimentation  against  tobacco  thrips 17-18 

Irrigation,  overhead,  remedy  for  tobacco  thrips 16 

Johnson  grass.  (See  Sorghum  halepense.) 

Kerosene  emulsion,  remedy  for  tobacco  thrips 18-21 

Leaf-miner.  (See  Phthorimcea  operculella.) 

Lime,  ineffective  against  tobacco  thrips 18 

Molasses,  ineffective  against  tobacco  thrips 18 

Mustard,  food  plant  of  tobacco  thrips 7,  11 

“ Nikoteen,”  against  tobacco  thrips 20 

Oats,  food  plant  of  Molothrips  bicolor  and  Anthothrips  niger 13 

Euthrips  tritici 12 

tobacco  thrips 11 

Onion,  food  plant  of  Thrips  tabaci 12 

thrips.  ( See  Thrips  tabaci. ) 

Orange,  food  plant,  of  Euthrips  tritici 12 

Phthorimcea  operculella,  on  tobacco 6 

Rain,  influence  on  tobacco  thrips 13-14 

Rose-leaf  insecticide,  against  tobacco  thrips 17 


23 


Paere. 

12 


Roses,  food  plants  of  Euthrips  tritici. 

Rubus  sp.  ( See  Dewberry.) 

Rye,  food  plant  of  tobacco  thrips Id 

Shepherd's  purse,  food  plant  of  tobacco  thrips 7. 11 

Sorghum  halepense,  food  plant  of  tobacco  thrips • 8 

Splitworm.  (See  Phthorimwa  operculella.) 

Spray,  for  tobacco  thrips,  no  injurious  effect  on  product 22 

Spraying,  for  tobacco  thrips*  cost 20-21 

Strawberry,  food  plant  of  Euthrips  tritici 12 

Suc-kfly.  (See  Dicyphus  minimus.) 

Temperatures,  in  slat  and  cheesecloth  shade  tobacco  fields,  difference 1G--17 

Thrips  tabaci  (onion  thrips)  mistaken  for  tobacco  thrips 12-1.*) 

on  tobacco  in  Russia 5 

tobacco.  (See  also  Euthrips  nicotianw.) 

cultural  methods  for  control 14—17 

distribution 7-8 

feeding  habits r 10-11 

flight 11 

food  plants __  7.11,10 

fungus  on  dead  specimens 14 

hibernation 12 

history  as  pest 5-0 

injury,  nature  and  extent 0-7 

insect  enemy •_ 14 

insecticides  used  in  experimentation 17-1S 

jumping 11 

life  history 11-12 

methods  for  study 11-12 

remedies 14-21 

species  mistaken  for  it 12-13 

spraying,  cost 20-21 

wheat.  (See  Euthrips  tritici.) 

Tobacco  decoction,  against  tobacco  thrips 18 

insect  enemies,  in  South ^ 0 

not  a food  plant  of  Thrips  tabaci  in  our  country 5 

presence  of  Anthothrips  niger 13 

thrips.  (Sec  Thrips,  tobacco,  and  Euthrips  nicotianw. ) 

Tomato,  presence  of  Anthothrips  niger _ 13 

Triphleps  insidiosus,  enemy  of  tobacco  thrips 14 

Whale-oil  soap,  against  tobacco  thrips 18 

Wheat,  food  plant  of  JEolothrips  bicolor  and  Anthothrips  niger 13 

tobacco  thrips __  11,10. 

thrips.  (See  Euthrips  tritici.) 

“ White  vein,”  injury  occasioned  by  tobacco  thrips 0-7 

A anthium  glabratum.  ( See  Cocklebur.) 


o 


UNIVERSITY  OF  ILLINOIS-URBANA 

630UN3ENN.S.  C003 

BULLETIN.  N.S.  WASHINGTON 
61-66  1906/07 


2 017670974 


